A field emission (FE) process is a phenomenon that a high-intensity electric field is applied on the surface of a metal or semiconductor and the like, and then electrons enter into vacuum by a tunnel effect. A cold cathode of the field emission has an advantage of low power consumption and rapid speed of response compared with a thermionic electron emission.
A high-melting-point metal such as Mo, W and semiconductor materials like Si are commonly adopted as an early field emission cathode material, and the cathode material is produced into a pointed cone shape so as to reduce an external electric field intensity needed. However, these cathode materials have disadvantages of low emission current, unstable performance, complex preparation process, and high cost, so these cathode materials cannot be applied in practice. A film edge structure has a greater field enhancement and a less screening effect than that a wedge structure, which is more beneficial for the field emission. Moreover, this structure is simpler than the wedge structure in terms of the production method and the process, but the process condition of the structure determines that an emitter of the structure usually lies flat on a substrate, which limits the range of application to some extent. If a nanostructure grows vertically on the substrate, the material will have a higher length-diameter ratio. This unique nanostructure has not only a high length-diameter ratio, but also a large specific surface area, so this nanostructure can become a good field emission material. In addition, since the edges of the two-dimensional materials, for example MoS2, consist of many electrons, the two-dimensional material of the nanostructure is considered as one of the most promising field emission materials.
Recently, crystalline materials of transition material chalcogenides (TMD), for example, MoS2, are highly valued in academia and industrial community. Although the materials have poor electron fluidity because a monomolecular layer of such materials has an intrinsic large band gap, mobility of the monolayer TMD material is greatly enhanced at room temperature by a gate of oxide layer medium during producing a transistor. Many unique electrical and optical properties are incarnated after degradation of bulk materials into monomolecular layer materials, and such materials become one of crucial materials in advanced international research of a new high-performance nanometer device. Besides an advantage of small volume, the TMD is lower in energy consumption than silicon widely used. The energy consumption of the field effect transistor prepared by TMD materials represented by the MoS2 is 100000 times less than a conventional silicon transistor under a stable state.
Currently, the preparation of the MoS2 film mainly focuses on mechanical exfoliation, liquid phase stripping and so on. However, the number of film layers prepared by this method is not controllable, and these layers all show a nanostructure such as a tiled MoS2 nanosheet, nanodisk, nanoline in a microcosmic view, and obtains a small area. The two-dimensional atomic crystalline material suitable for high-property field emission devices has rarely been studied.